Skyhook has tried before to land Google in trouble by alleging in a Massachusetts court that the web goliath's Android operating system forces mobile phone users to use its location-finding services instead of Skyhook's as well as the infringement of four patents.

Now Skyhook, which maps Wi-Fi base stations to their physical locations, has filed a lawsuit in Delaware with a new set of patent claims. It demands a permanent injunction on Google Maps as well as damages. All nine patents deal with geo-location from nearby WLAN access points, a popular technique for position-finding because it can work inside buildings where GPS satellite signals are hard to pick up, and also because the limited range of WLANs offers a fairly precise location compared to the wide-ranging area covered by a mobile mast. Use of wireless signals also avoids or minimises the power drain of GPS receivers.

Skyhook was an early mover in the field of wireless location, and its services were used at times by major players such as Apple. But nowadays every Android phone - unless the user opts out of radio location - acts as a mobile sensor, continually sniffing for new radio signals as it moves about and sending the info back to Google's databases, which are also fed by the company's Street View slurpcar fleet. The Chocolate Factory has long since moved past any need to use Skyhook's services.

Now Skyhook claims that Google wilfully infringed on its patents, which it found out about during talks between the two companies. Google's map app - which was recently thrown off Apple's iOS platform - can look to nearby Wi-Fi networks to work out where the user is, provided the networks' locations are known to the search engine.